Another very important argument for the use of uniform knowledge sources is the possibility of modelling the assumption that during communication the use of language of one interlocutor is influenced by means of the language use of the others (see also [Neumann1991a, Neumann1991b]).
For example, in a uniform lexicon it does not matter whether a lexeme was accessed during parsing or generation. This means that the use of linguistic elements of the interlocutor influences the choice of lexical material during generation (if the frequency of lexemes serves as a decision criterion). This will help to choose between lexemes which are synonymous in the actual situation or when the semantic input cannot be sufficiently specified. For example, some containers can be denoted either `cup' or `mug' because their shape cannot be interpreted unequivocally. An appropriate choice would be to use the same lexeme that was previously used by the interlocutor (if no other information is available), in order to ensure that the same object will be denoted. In principle this is also possible for the choice between alternative syntactic structures.
This adaptation to the partner's use of language in communication is one of the sources for the fact that the global generation process of humans is flexible and efficient. Of course, adaptability is also a kind of co-operative behaviour. This is necessary, if new ideas have to be expressed for which no mutually known linguistic terms exist (e.g., during communication between experts and novices). In this case adaptability to the hearer's use of language is necessary in order to make it possible for the hearer to understand the new information.
In principle this kind of adaptability means that the input structures computed during the understanding process carry some information that can be used to parameterize the generation process. This leads to more flexibility: not all necessary parameters need to be specified in the input of a generator because decision points can also be set during run-time.
This dynamic behaviour of a generation system will increase efficiency, too. As McDonald et al. McDonaldetal:87 define, one generator design is more efficient than another, if it is able to solve the same problem with fewer steps. They argue that ``the key element governing the difficulty of utterance production is the degree of familiarity with the situation.'' The efficiency of the generation process depends on the competence and experience one has acquired for a particular situation. But to have experience in the use of linguistic objects that are adequate in a particular situation means to be adaptable.